The present invention relates generally to methods and apparatus for absorbing shock, and more particularly relate to methods and apparatus for absorbing shock in equipment utilized in earth boreholes in the oil and gas industry.
In many applications in the oil and gas industry, there is a need to protect systems utilized in earth boreholes from shock. For example, one such application is during the completion or testing of oil and gas wells, when the wells are either completed or tested through the use of perforating guns. In a common type of well completion operation, a perforating gun will be run into an earth borehole on the tubing string. In addition to the perforating gun, it is not uncommon to include other equipment for controlling or monitoring the well during the completion operation. For example, measurement devices such as temperature and pressure recorders may be included in the tool string. Additionally, the tool string may include other equipment associated with the well completion or testing operation, such as gravel packing tools, vent assemblies or packers.
The performating guns typically carry a plurality of explosives, such as shaped charges, designed to penetrate the earth formation surrounding the borehole. The detonation of these explosives will generate a reaction or "recoil" in the tool string which will tend to accelerate the string both radially, or horizontally, within the borehole, as well as longitudinally, or vertically, within the borehole. Accelerations of the tool string can be both high and low frequency. Acoustic vibrations can be transmitted both directly through the tool string to a vibration sensitive component or may be transmitted through borehole fluids to components in the tool string.
When the tool string includes additional devices, as described above, the shock transmitted to the string, either directly or indirectly, at the time of the detonation of the perforating gun increases the likelihood of damage to the devices. This is particularly true in the case of relatively delicate instruments such as the pressure or temperature recorders described above, or such as various types of electronic equipment which may be utilized within the well.
Accordingly, the present invention provides a new method and apparatus for isolating and absorbing shock in a borehole environment. The method and apparatus of the present invention are believed to have particular applicability in minimizing the transmission of shock caused by the detonation of tubing-conveyed perforating guns from the tubing string and other equipment in the tool string.